U.S. Pat. No. 3,826,179 issued July 30, 1974 discloses a damper system including a plurality of blades which are resiliently biased into closed position. This device is utilized to equalize the pressure in buildings in an area where tornadoes frequently occur. This damper system is not located generally adjacent rooms to be heated or cooled by a heating or air conditioning system. It is used to equalize external pressure from outside the building with pressure inside the building, rather than to maintain heated or cooled air within a room which has been supplied with the heated or cooled air.